Backlight unit for liquid crystal display

ABSTRACT

The invention provide a cost effective way of determining the status of a light emitting device, such as a light emitting device in a non-emitting display device. The apparatus includes a plurality of light emitting devices arranged in a predefined configuration, a voltage supply coupled to the light emitting devices for making a current flow through the light emitting devices, and electrically conductive devices positioned a predetermined distance away from the light emitting devices, wherein each of the electrically conductive devices generates a voltage in response to current flowing through one of the light emitting devices. An AND gate coupled to the electrically conductive devices receives the voltage from each of the electrically conductive devices through an input and generates an output. A status determining device coupled to the output of the AND gate determines the status of the light emitting devices based on this output.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a backlight unit for a liquid crystaldisplay.

(b) Description of Related Art

Display screens, such as computer and television monitors, are usuallymade of either self-emitting displays or non-emitting displays. Examplesof self-emitting displays include light emitting diodes (LEDs),electroluminescences (ELs), vacuum fluorescent displays (VFDs), fieldemission displays (FEDs) and plasma display panels (PDPs). A commonlyused non-emitting display includes liquid crystal displays (LCDs).Non-emitting displays, unlike self-emitting displays, require a lightsource.

An LCD includes two panels coupled with field-generating electrodes anda liquid crystal (LC) layer with dielectric anisotropy interposedtherebetween. When electric voltages are applied to the field-generatingelectrodes, an electric field is generated in the liquid crystal layerin response to the voltages. Light transmittance through the LC layervaries depending on the electric field. Thus, light transmittance iscontrolled by varying the applied voltages. By manipulating the appliedvoltages, desired images are displayed on the liquid crystal display.

The LCD being a non-emitting type of display, the light that is used todisplay the images is supplied by a separate source. This separatesource may be an artificial light source such as a lamp coupled to theLCD, or a natural source like the sun. When using an artificial lightsource, the total brightness of the LCD screen is usually adjusted byeither using an inverter to regulate the ratio of the on and off signalssupplied to the light source or by regulating the current through thelight source.

Typically, a large LCD requires several light sources (e.g., lamps) foruniform luminance across the LCD. When several lamps are used, the lampsare driven by a driving circuit, such as an inverter, for costefficiency. When multiple lamps are used, however, there is a downsideof not being able to easily detect a malfunctioning of one of the lamps,which may be caused by the one lamp being improperly mounted or simplydefective. Malfunctioning of one lamp is highly undesirable as it maycause arcs near electrodes of the lamp. Aside from being a visualimperfection on the display, the arcs can pose a hazard by causing fire.A method of detecting a malfunctioning lamp is desired.

SUMMARY OF THE INVENTION

The invention provides a method and apparatus for determining the statusof a light emitting device (e.g., a lamp) in a cost effective manner,allowing a prompt detection of an incorrectly mounted or defective lightemitting device. The apparatus includes a light emitting device, avoltage supply coupled to the light emitting device for making a currentflow through the light emitting device, an electrically conductivedevice positioned a predetermined distance away from the light emittingdevice for generating a voltage in response to the current flowingthrough the light emitting device, and a status determining device fordetermining the status of the light emitting device based on the voltagefrom the electrically conductive device.

In another aspect, the apparatus includes a plurality of light emittingdevices arranged in a predefined configuration, a voltage supply coupledto the light emitting devices for making a current flow through thelight emitting devices, a plurality of electrically conductive devicespositioned a predetermined distance away from the light emittingdevices, wherein each of the electrically conductive devices generates avoltage in response to current flowing through one of the light emittingdevices, an AND gate coupled to the electrically conductive devices suchthat the voltage from each of the electrically conductive devices formsan input to the AND gate, the AND gate generating an output, and astatus determining device coupled to the output of the AND gate todetermine the status of the light emitting device based on the output.

The invention also includes a liquid crystal display device including aliquid crystal display panel, electrodes for generating an electricfield in the liquid crystal display panel, and one of the aboveapparatuses.

The method of the invention includes generating a voltage in response toa current flowing through each of the light emitting devices, processingthe voltage of the light emitting devices to generate an output voltage,and determining whether any of the light emitting devices is in anabnormal operational state based on the output voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more apparent by describing preferredembodiments thereof in detail with reference to the accompanyingdrawings in which:

FIG. 1 is an exploded perspective view of an LCD according to anembodiment of the present invention;

FIG. 2 is a section view of a backlight assembly for an LCD according toan embodiment of the present invention;

FIG. 3 is a front view of the backlight assembly shown in FIG. 2;

FIG. 4 illustrates an experiment for measuring a voltage induced in ametal sheet in the backlight assembly shown in FIGS. 2 and 3;

FIG. 5 is a circuit diagram of a backlight unit for an LCD according toanother embodiment of the present invention;

FIGS. 6A and 6B show waveforms of signals in the backlight unit shown inFIG. 5 for a normal operation and an abnormal operation, respectively;and

FIG. 7 is a circuit diagram of a backlight unit for an LCD according toanother embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Like numerals refer to like elementsthroughout.

In the drawings, the thickness of layers and regions are exaggerated forclarity. Like numerals refer to like elements throughout. It will beunderstood that when an element such as a layer, region or substrate isreferred to as being “on” another element, it can be directly on theother element or intervening elements may also be present. In contrast,when an element is referred to as being “directly on” another element,there are no intervening elements present. Likewise, when an element isreferred to as being “coupled to” another element, the elements may bedirectly connected or connected through one or more interveningelements.

Backlight units for a liquid crystal display will be described in detailwith reference to the accompanying drawings.

FIG. 1 is an exploded perspective view of an LCD according to anembodiment of the present invention.

An LCD 900 according to an embodiment of the present invention includesan LC module 700 including a display unit 710 and a backlight unit 720,a pair of front and rear cases 810 and 820, a chassis 740, and a moldframe 730. The mold frame 730 hold the LC module 700 together by framingits components, as shown in FIG. 1.

The display unit 710 includes the LC panel assembly 712, a plurality ofgate tape carrier packages (TCPs) 718, a plurality of data TCPs 716attached to the LC panel assembly 712, a gate printed circuit board(PCB) 719, and a data PCB 714 attached to the associated TCPs 718 and716, respectively.

The LC panel assembly 712, in structural view shown in FIG. 1, includesa lower panel 712 a, an upper panel 712 b and a liquid crystal layer(not shown) interposed therebetween while it includes a plurality ofdisplay signal lines (not shown) and a plurality of pixels (not shown)connected thereto and arranged substantially in a matrix.

The display signal lines are provided on the lower panel 712 a andinclude a plurality of gate lines (not shown) transmitting gate signals(called scanning signals) and a plurality of data lines (not shown)transmitting data signals. The gate lines extend substantially in a rowdirection and are substantially parallel to each other, while the datalines extend substantially in a column direction and are substantiallyparallel to each other.

Each pixel includes a switching element connected to the display signallines, an LC capacitor, and a storage capacitor that are connected tothe switching element. The storage capacitor may be omitted ifunnecessary.

The switching element (e.g., a TFT) is provided on the lower panel 712 aand has three terminals: a control terminal connected to one of the gatelines, an input terminal connected to one of the data lines, and anoutput terminal connected to the LC capacitor and the storage capacitor.

The LC capacitor includes a pixel electrode (not shown) on the lowerpanel 712 a, a common electrode (not shown) on the upper panel 712 b,and the LC layer as a dielectric between the electrodes. The pixelelectrode is connected to the switching element and preferably made oftransparent conductive material such as indium tin oxide (ITO) andindium zinc oxide (IZO) or reflective conductive material. The commonelectrode covers the entire surface of the upper panel 712 a and ispreferably made of transparent conductive material such as ITO and IZOand supplied with a common voltage. Alternatively, both the pixelelectrode and the common electrode, which are shaped and arranged likebars or stripes, are provided on the lower panel 712 a.

The storage capacitor is an auxiliary capacitor for the LC capacitor.The storage capacitor includes the pixel electrode and a separate signalline (not shown), which is provided on the lower panel 712 a, overlapsthe pixel electrode via an insulator, and is supplied with apredetermined voltage such as the common voltage. Alternatively, thestorage capacitor includes the pixel electrode and an adjacent gate linecalled a previous gate line, which overlaps the pixel electrode via aninsulator.

For color display, each pixel represents its own color by providing oneof a plurality of red, green and blue color filters in an area occupiedby the pixel electrode. The color filter is provided in thecorresponding area of the upper panel 712 b. Alternatively, the colorfilter is provided on or under the pixel electrode on the lower panel712 a.

Referring to FIG. 1, the backlight unit 720 includes a plurality oflamps 725 disposed under the LC panel assembly 712, a light guide 724and a plurality of optical sheets 726 disposed between the panelassembly 712 and the lamps 725 for guiding and diffusing light from thelamps 725 to the panel assembly 712, and a reflector 728 disposed underthe lamps 725 for reflecting the light from the lamps 725 toward thepanel assembly 712.

The light guide 724 has uniform thickness, and the number of the lamps725 is determined in consideration of the operation of the LCD. Thelamps 725 preferably include fluorescent lamps such as CCFL (coldcathode fluorescent lamp) and EEFL (external electrode fluorescentlamp). An LED is another example of the lamp 725.

A pair of polarizers (not shown) polarizing the light from the lamps 725are attached on the outer surfaces of the panels 712 a and 712 b of thepanel assembly 712.

The TCPs 716 and 718 are flexible printed circuit (FPC) films that areattached to the edges of the LC panel assembly 712. A plurality of datadriving integrated circuit (IC) chips connected to the data lines of theLC panel assembly 712 and applying data voltages thereto are mounted onthe data TCP 716. Similarly, a plurality of gate driving IC chipsconnected to the gate lines of the LC panel assembly 712 and applyinggate voltages thereto after combining a gate-on voltage and a gate-offvoltage are mounted on the data TCP 718.

The PCBs 714 and 719 are connected to the TCPs 716 and 718 and includecircuit elements for receiving image signals and input control signalsfor controlling the image signals, processing the image signals, andgenerating output control signals for the processed image signals to beprovided for the driving ICs on the TCPs 716 and 718.

According to other embodiments of the present invention, the gatedriving circuits and/or the data driving circuits are chip-mounted onthe lower panel 712 a, while one or both of the driving circuits areincorporated along with other elements into the lower panel 712 a. Thegate PCB 719 and/or the gate FPC films 718 may be omitted in both cases.

A backlight assembly for an LCD according to an embodiment of thepresent invention will be described in detail with reference to FIGS.2–4.

FIG. 2 is a section view of a backlight assembly for an LCD according toan embodiment of the present invention, and FIG. 3 is a front view ofthe backlight assembly shown in FIG. 2.

Referring to FIGS. 2 and 3, a backlight assembly for an LCD according toan embodiment of the present invention includes a reflector 2, aplurality of lamps 1 spaced apart from a front surface of the reflector2 and arranged parallel to each other, and a plurality of metal sheets 3located on a rear surface of the reflector 2. The number of the metalsheets 3 is equal to the number of the lamps 1, and the metal sheets 3are aligned with the respective lamps 1. Each lamp 1 and thecorresponding metal sheet 3 are spaced apart from each other by adistance d as shown in FIG. 2.

The lamps 1 are external electrode fluorescent lamps (EEFLs), eachincluding a tube and a pair of electrodes provided external to the tube.However, the lamps 1 may be other types of lamps such as cold cathodefluorescent lamp (CCFLs).

The backlight assembly according to this embodiment adopts a floatingapplication that applies positive and negative voltages to bothterminals of the lamps 1.

Upon application of AC voltages to both terminals of the lamps 1, eachlamp 1 acts as a resistor to flow high current, and emits light. Avoltage proportional to the voltage across the lamp 1 is induced in themetal sheet 3 spaced apart from the lamp 1 by the distance d since themetal sheet 3 and the lamp 1 act as a capacitor. If the lamp 1 operatesin abnormal state due to some reasons such as improper mounting of thelamp 1 or breakage of the lamps 1, the induced voltage in the metalsheet 3 is likely to be very low, perhaps even nonexistent. The distanced is preferably selected so that very little voltage induction occursfrom adjacent lamps 1. Thus, the operational state or status of thelamps 1 can be determined by measuring the voltages induced in the metalsheets 3.

FIG. 4 illustrates an experiment that was conducted to test thecorrelation between the status of a lamp and the voltage induced in ametal sheet near the lamp in the backlight assembly of FIGS. 2 and 3.

Referring to FIG. 4, an AC voltage Vs was applied across a plurality oflamps 1 including the lamp 1 a that is shown, and a voltmeter M wasconnected to a metal sheet 3 a, which is one of the metal sheets 3 thatis spaced apart from the lamp 1 a by a predetermined distance. Thevoltage of the metal sheet 3 a measured by the voltmeter M wasproportional to the voltage across the lamp 1 a when the lamp 1 anormally operated. When the voltage Vs was cut off from all the lamps,no voltage was measured by the voltmeter M. When the voltage Vs wassupplied to all the lamps 1 except for the lamp 1 a, the measuredvoltage of the metal sheet 3 a was very small. Accordingly, it isexpected that there is, at most, a very small induced voltage in themetal sheet 3 a due to the parasitic coupling capacitance betweenadjacent lamps 1 and the metal sheet 3 a if there is no current in thelamp 1 a caused by the turning off, releasing, and cutting off, etc., ofthe lamp 1 a.

A backlight unit for an LCD according to another embodiment of thepresent invention will be described in detail with reference to FIGS. 5,6A and 6B.

FIG. 5 is a circuit diagram of a backlight unit for an LCD according toanother embodiment of the present invention, and FIGS. 6A and 6B showwaveforms of signals in the backlight unit shown in FIG. 5 for a normaloperation and an abnormal operation, respectively.

Referring to FIG. 5, a backlight unit for an LCD according to anotherembodiment of the present invention includes a transformer T suppliedwith an AC voltage VH and VL, a plurality of lamps 1 connected acrossthe transformer T, a plurality of metal sheets 3 spaced apart from therespective lamps 1, a plurality of rectifier circuits 4 connected to therespective metal sheets 3, a plurality of RC filters 5 connected to therespective rectifier circuits 4, an AND gate 6 connected to the RCfilters 5, a dimming error prevention circuit 7, and a time constantdetermining circuit 8. Preferably, the number of the metal sheets 3 isequal to the number of the lamps 1.

When the voltage VH and VL is applied to the lamps 1 through thetransformer T, the lamps 1 start lighting and AC voltages havingmagnitudes proportional to a magnitude of the AC voltage VH and VLapplied to the lamps 1 are induced in the corresponding metal sheets 3as shown in FIGS. 6A and 6B.

As shown in FIGS. 6A and 6B, the rectifier 4 half-wave rectifies asignal from the metal sheet 3 as shown in FIGS. 6A and 6B, and the RCfilter 5 removes ripples from the rectified signal output from therectifier circuit 4 to convert the rectified signal into a stable DCsignal.

In the embodiment of FIG. 5, the rectifier circuit 4 includes a diode D1connected in reverse direction from the metal sheets 3, another diodeconnected in forward direction from the metal sheets 3, and a resistorR1 connected to the diode D2 for forming a current path. The diode D1cuts off a negative component of the signal from the respective one ofthe metal sheets 3 that is connected to the rectifier circuit 4, whilethe diode D2 passes a positive component of the signal from the metalsheet. Accordingly, the rectifier circuit 4 passes only the positivecomponent of the voltage signal induced in the metal sheet, effectuatinga half-wave rectification.

The RC filter 5 receives the rectified signal outputted from therectifier 4 through a node between the diode D2 and the resistor R1.

The RC filter 5 includes a resistor R2 and a capacitor C1 connected inseries. The positive component of the voltage signal from the metalsheets 3 passes through the diode D2 and passes through a path includingthe resistor R1 and another path including the resistor R2 and thecapacitor C1 of the RC filter 5. The positive voltage signal is chargedin the capacitor C1 to be converted into an output DC voltage OUT1.Appropriate selection of the resistance of the resistor R2 and thecapacitance of the capacitor C1 may yield the output voltage OUT1 ofabout 3.5V to 5V during the normal lighting operation of the lamp 1 asshown in FIG. 6A.

There are three operational states of the lamps 1: a normal activestate, a normal inactive state, and an abnormal inactive state. Thelamps 1 are driven to be turned on and turned off periodically bypulse-width modulation (PWM) dimming control with a predetermined on/offduty ratio. When the lamps 1 are in the normal or abnormal inactivestate, the output voltage OUT1 reaches zero or a little value equal toor smaller than 1.2V as shown in FIG. 6B, which may be resulted fromcurrent leakage. Accordingly, the normal activation of the lamp 1 can bedetermined based on the output voltage OUT1 of the RC filter 5.

The output voltages OUT1–OUT4 of the RC filters 5 for the lamps 1 formthe input signals to the AND gate 6, which performs the well-known ANDoperation on input signals and generates an output signal to be suppliedto a status determining device including a shut down terminal, SDOWN.This output signal is sent through an output resistor R3 located betweenthe AND gate 6 and the shut down terminal SDOWN. The threshold voltageof the AND gate 6 is set to be about 2.5V such that the AND gate 6generates a high level output when all the input signals are equal to orhigher than 2.5V while it generates a low level output when any one ofthe input signals are smaller than 2.5V. Accordingly, if any one of thelamps 1 is inactive, the output of the AND gate 6 drops to a level belowthe threshold voltage. The shut down terminal SDOWN cuts off the supplyvoltage to the lamps 1. A person of ordinary skill in the art willappreciate that the predefined ranges for delineating the high voltagelevel and the low voltage level, as well as the threshold voltage level,may be adjusted as appropriate.

One concern with the shut down terminal cutting off the supply voltageupon detecting a low output voltage is that the supply voltage becomesundesirably cut off when the lamps 1 are in the normal inactive state.While it is desirable to cut off the supply voltage only when the lamps1 are in the abnormal state, the shut down terminal SDOWN cannotdistinguish between a normal inactive state and an abnormal inactivestate, since both states cause a drop in the output voltage level.

This concern is addressed by a dimming error prevention circuit 7. Thedimming error prevention circuit 7 provides a high voltage signal to theshut down terminal SDOWN in response to a PWM dimming signal DIM, whichhas an on section and an off section when the lamps 1 are in the normalinactive state. The normally operating lamps 1 turn on during the onsection of the dimming signal DIM, while they turn off during the offsection of the dimming signal DIM. The dimming error prevention circuit7 outputs the high voltage level signal during the off section of thedimming signal DIM. This high voltage output by the dimming errorprevention circuit 7 prevents the shut down terminal frommisinterpreting a normal inactive state as an abnormal inactive state,by effectively disguising the normal inactive state as a normal activestate.

The dimming error prevention circuit 7 includes a transistor Q and aninput resistor R4. The transistor Q is a pnp bipolar transistor havingan emitter connected to a supply voltage VCC (herein also referred to as“an alternative supply voltage”), a base connected to the input resistorR4, and a collector connected to a shut down terminal SDOWN through anoutput resistor R6.

The dimming control signal DIM is fed into the base of the transistor Qthrough the input resistor R4. The transistor Q turns off during the onsection of the dimming control signal DIM and, in this case, the outputof the AND gate 6 is detected by the shut down terminal SDOWN withoutcontribution from the dimming error prevention circuit 7. On thecontrary, the transistor Q turns on during the off section of thedimming control signal DIM such that the supply voltage VCC of highlevel is supplied for the shut down terminal SDOWN. In this case, theshut down terminal SDOWN knows to ignore the low voltage output of theAND gate 6. As a result, the dimming error prevention circuit 7 enforcesa high level signal to be detected by the shut down terminal when one ormore of the lamps 1 are in the normal inactive state.

The lamps' transition from an active state to an inactive state, andvice versa, is not instant. Thus, a certain amount of time is needed forthe lamps 1 to transition between the normal inactive state and thenormal active state. When the lamps 1 first receive a transition signalto transition from the inactive state to the active state, it isdesirable for the shut down signal to reflect this transition as soon aspossible. Otherwise, the transition phase may be interpreted as anabnormal inactive state. Thus, a mechanism is required to maintain theoutput signal from the AND gate 6 at a high level while the lamps 1transition.

A time constant determining circuit 8 shown in FIG. 5 delays an initiallighting signal BL_ON for the backlight unit during the transition ofthe lamps 1 and includes a capacitor C2 and a resistor R5 connected inparallel. The capacitance of the capacitor C2 and the resistance of theresistor R5 are determined such that the time constant preferably rangesabout 0.3 seconds to about one second. As a result, the time constantdetermining circuit 8 provides a high level signal to the shut downterminal during the transition of the lamps 1 from an inactive state toan active state.

A backlight unit for an LCD according to another embodiment of thepresent invention is now described in detail with reference to FIG. 7.

FIG. 7 is a circuit diagram of a backlight unit for an LCD according toanother embodiment of the present invention.

The backlight unit according to this embodiment directly detectsvoltages induced in metal sheets 3 and determines an abnormal state oflamps 1.

A backlight unit according to this embodiment includes a transformer T,a plurality of lamps 1, a plurality of metal sheets 3, a plurality ofrectifier circuits 41, a plurality of RC filters 51, an AND gate 6, adimming error prevention circuit 7, and a time constant determiningcircuit 8. The detailed configurations of the above-described elementsare similar to those shown in FIG. 5 except for the rectifier circuits41 and the RC filters 51.

The rectifier circuit 41 includes a diode D3 connected in forwarddirection from the metal sheet 3 to the RC filter 51, and the RC filter51 includes a resistor R2 and a capacitor C1 connected in series.

A positive component of a voltage signal induced in the metal sheet 3passes through the diode D3 and is charged in the capacitor C1.Accordingly, the output voltage OUT1 of the capacitor C1 represents a DClevel of the positive component of the induced voltage and is inputtedto the AND gate 6. The AND gate 6 performs an AND operation on inputsfrom the RC filters 51 connected to the metal sheets 3 and generates anoutput to be provided as a shut down signal.

As described above, backlight units according to embodiment of thepresent invention detect voltages induced in metal sheets, which areprovided at respective lamps driven by an AC voltage, therebydetermining whether the lamps operate in a normal condition.Accordingly, when the lamps are not properly mounted or when the lampsperforms malfunction during the lighting, the power supply for thebacklight unit can be blocked to remarkably reduce the occurrence ofarcs near lamp electrodes and the occurrence of defects in productassembly.

Although preferred embodiments of the present invention have beendescribed in detail hereinabove, it should be clearly understood thatmany variations and/or modifications of the basic inventive conceptsherein taught which may appear to those skilled in the present art willstill fall within the spirit and scope of the present invention, asdefined in the appended claims.

For example, in an alternative embodiment, only some of the multiplelamps in a device have a metal sheet 3. This alternative embodiment maybe useful if there is a subgroup of lamps that are critical to theoperation of the display device and only this subgroup is to bemonitored.

1. An apparatus for checking a status of a light emitting device, theapparatus comprising: a light emitting device; a voltage supply coupledto the light emitting device for making a current flow through the lightemitting device; an electrically conductive device spaced apart from thelight emitting device for generating a voltage in response to thecurrent flowing through the light emitting device; a status determiningdevice for determining the status of the light emitting device based onthe voltage from the electrically conductive device; and a rectifiercircuit having a first node and a second node, wherein the first node isconnected to the electrically conductive device and the second node isconnected to a signal detector, wherein the voltage supply is an ACvoltage supply, further comprising an RC filter circuit for convertingan output from the rectifier circuit into a DC signal, wherein the RCfilter circuit is connected to the rectifier circuit and the signaldetector.
 2. An apparatus for checking a status of a light emittingdevice, the apparatus comprising: a light emitting device; a voltagesupply coupled to the light emitting device for making a current flowthrough the light emitting device; an electrically conductive devicespaced apart from the light emitting device for generating a voltage inresponse to the current flowing through the light emitting device; and astatus determining device for determining the status of the lightemitting device based on the voltage from the electrically conductivedevice, wherein the voltage having a level below a threshold valueindicates that the light emitting device is operating abnormally, and adimming error prevention circuit coupled to a node between theelectrically conductive device and the status determining device,wherein the dimming error prevention circuit is for connecting thestatus determining device to an alternative voltage supply if the lightemitting device is in a normal inactive state, so as to prevent thestatus determining device from interpreting the voltage generated by thelight emitting device in a normal inactive state as the light emittingdevice being in an abnormal inactive state.
 3. The apparatus of claim 2,wherein the dimming error prevention circuit comprises: a transistor; analternative voltage source coupled to the transistor; and a dimmingsignal source coupled to the base of the transistor and generating an“on” signal upon detecting that the light emitting device is in a normalinactive state; wherein the transistor is configured to connect thealternative voltage source to the status determining device in responseto the “on” signal from the dimming signal source.
 4. The apparatus ofclaim 2, wherein the dimming error prevention circuit comprises atransistor for supplying an alternative voltage to the statusdetermining device upon receiving a signal indicating that the lightemitting device is in a normal inactive state.
 5. The apparatus of claim2 further comprising a time constant determining circuit coupled to thenode for creating a delay in the dimming error prevention circuit'sdisconnecting of the alternative voltage supply from the statusdetermining device upon the light emitting device's transition betweenan inactive state and a normal active state.
 6. An apparatus forchecking a status of a light emitting device, the apparatus comprising:a plurality of light emitting devices arranged in a predefinedconfiguration; a voltage supply coupled to the light emitting devicesfor making a current flow through the light emitting devices; aplurality of electrically conductive devices positioned a predetermineddistance away from the light emitting devices, wherein each of theelectrically conductive devices generates a voltage in response tocurrent flowing through one of the light emitting devices; an AND gatecoupled to the electrically conductive devices such that the voltagefrom each of the electrically conductive devices forms an input to theAND gate, the AND gate generating an output; and a status determiningdevice coupled to the output of the AND gate to determine the status ofthe light emitting device based on the output.
 7. The apparatus of claim6, wherein the status determining device comprises a means for stoppingthe current from flowing through the light emitting devices if theoutput of the AND gate fulfills a predefined condition.
 8. The apparatusof claim 6 further comprising a plurality of rectifier circuits, whereineach of the rectifier circuits is coupled to one of the electricallyconductive devices and to the AND gate.
 9. The apparatus of claim 8,wherein the voltage supply is an AC voltage supply, further comprising aplurality of conversion circuits for receiving an AC signal from therectifier circuits and generating a DC voltage for inputting into theAND gate.
 10. The apparatus of claim 9, wherein the conversion circuitscomprise an RC filter.
 11. The apparatus of claim 10 further comprisinga dimming error prevention circuit coupled to a node between the ANDgate and the status determining device, wherein the dimming errorprevention circuit is for connecting the status determining device to analternative voltage supply if at least one of the light emitting devicesis in a normal inactive state, so that the status determining devicereceives a different output voltage from the AND gate when one of thelight emitting devices is in a normal inactive state than when one ofthe light emitting devices is in an abnormal inactive state.
 12. Theapparatus of claim 11, wherein the dimming error prevention circuitcomprises: a transistor; an alternative voltage source coupled to thetransistor; and a dimming signal source coupled to the base of thetransistor and generating an “on” signal upon detecting that the lightemitting device is in a normal inactive state; wherein the transistor isconfigured to connect the alternative voltage source to the statusdetermining device in response to the “on” signal from the dimmingsignal source.
 13. The apparatus of claim 11, wherein the dimming errorprevention circuit comprises a transistor for supplying an alternativevoltage to the status determining device upon receiving a signalindicating that the light emitting device is in a normal inactive state.14. The apparatus of claim 11 further comprising a time constantdetermining circuit coupled to the node for creating a delay in thedimming error prevention circuit's disconnecting of the alternativevoltage supply from the status determining device upon the lightemitting device's transition between an inactive state and a normalactive state.
 15. A method of checking a status of a light emittingarray, wherein the light emitting array includes a plurality of lightemitting devices, the method comprising: generating a voltage inresponse to a current flowing through each of the light emitting devicesby using an electrically conductive device spaced apart from the lightemitting device; processing the voltage of the light emitting devices togenerate an output voltage; determining whether any of the lightemitting devices is in an abnormal operational state based on the outputvoltage; and stopping the current flowing through each of the lightemitting devices upon determining that at least one of the lightemitting devices is in an abnormal operational state.
 16. A liquidcrystal display device comprising: a liquid crystal display panel;electrodes for generating an electric field in the liquid crystaldisplay panel; and a backlight assembly including; a first lightemitting device; a voltage supply coupled to the light emitting devicefor making a first current flow through the first light emitting device;a first electrically conductive device spaced apart from the lightemitting device for generating a first voltage in response to the firstcurrent flowing through the first light emitting device; a statusdetermining device for determining the status of the light emittingdevice based on the first voltage from the electrically conductivedevice; a second light emitting device coupled to the voltage supply formaking a second current flow through the second light emitting device; asecond electrically conductive device positioned for generating a secondvoltage in response to the second current; and an AND gate receiving thefirst voltage and the second voltage and generating an output voltage,wherein the output voltage is coupled to the status determining device,which determines the status based on the output voltage of the AND gate.17. The liquid crystal display device of claim 16 further comprising adimming error prevention circuit coupled to a node between the AND gateand the status determining device, wherein the dimming error preventioncircuit comprises: a transistor; an alternative voltage source coupledto the transistor; and a dimming signal source coupled to the base ofthe transistor and generating an “on” signal upon detecting that thelight emitting device is in a normal inactive state; wherein thetransistor is configured to connect the alternative voltage source tothe status determining device in response to the “on” signal from thedimming signal source.
 18. The liquid crystal display device of claim 16further comprising a dimming error prevention circuit coupled to a nodebetween the AND gate and the status determining device, wherein thedimming error prevention circuit comprises a transistor for supplying analternative voltage to the status determining device upon receiving asignal indicating that the light emitting device is in a normal inactivestate.
 19. The liquid crystal display device of claim 18 furthercomprising a time constant determining circuit coupled to the node forcreating a delay in the dimming error prevention circuit's disconnectionof the alternative voltage from the status determining device when thelight emitting device transitions between an inactive state and a normalactive state.